An organic semiconductor substrate includes a base, a first conductive pattern, a second conductive pattern, a first metal oxide pattern, a second metal oxide pattern, an organic flat pattern layer, a source, a drain, an organic semiconductor pattern, an organic gate insulating layer, and a gate. The first conductive pattern and the second conductive pattern are disposed on the base and separated from each other. The first metal oxide pattern and the second metal oxide pattern respectively cover and are electrically connected to the first conductive pattern and the second conductive pattern, respectively. A first portion of the organic flat pattern layer is disposed between the first metal oxide pattern and the second metal oxide pattern. A surface of the first metal oxide pattern has a first distance from the base. A surface of the first portion of the organic flat pattern layer has a second distance from the base. The second distance is less than or equal to the first distance.